The present invention is directed generally to fluorometric analyzers, and more particularly to an improved head assembly for a fluorometer wherein the photomultiplier tube of the analyzer is protected against exposure to incident and reflected ambient light.
Fluorometric analyzers such as the Fluoro-Monitor and Fluoro-Colorimeter (Trademarks) manufactured by the American Instrument Company Division of Baxter Travenol Laboratories, Inc. find wide application in detecting fluorescence in liquid samples. In these instruments the samples are exposed through an appropriate filter to radiation from an excitation lamp light source, and fluorescence within the sample is detected by a detector in the form of a photomultiplier tube disposed at right angles to the direction of excitation. In the Fluoro-Monitor analyzer, the excitation lamp, test cell, photomultiplier tube and filter are incorporated in a compact head assembly which provides for the shortest possible optical paths between the light source, sample and detector for optimum analyzer sensitivity. This head assembly is described in U.S. Pat. No. 3,917,404, which issued to the present inventor on Nov. 4, 1975 and is assigned to the present assignee.
In fluorometric analyzer head assemblies the liquid sample being analyzed may be contained in either a closed-end cuvette, wherein a specific quantity of liquid is observed, or in an open-ended flow cell, wherein a continuous flow of liquid is observed. Where individual cuvettes are being analyzed, the possibility exists of the sensitive photomultiplier tube being exposed to ambient light, either directly or as a result of reflections when the cuvettes are being changed. Where a flow-cell is being utilized, the possibility for such exposure also exists while changing or adjusting the flow cell, or when it becomes necessary to correct a leaking connection with associated tubing. Exposure of the sensitive photomultiplier tube to the relatively strong incident or reflected light has the effect of reducing the photomultiplier tube sensitivity for a period of time, making subsequent measurements inaccurate and requiring the operator to wait for the detector to restabilize before proceeding with a measurement.
Prior-art fluorometric analyzer head assemblies, such as that of the aforementioned Fluoro-Monitor analyzer, incorporated a shutter for the excitation lamp which could be conditioned to block light rays from reaching the sample. While effective for this purpose, the shutter did not prevent ambient light from reaching the photomultiplier tube upon removal of the test cell. In bioluminescence applications wherein no excitation light source is utilized, such as those described in Bergmeyer, Methods of Enzymatic Analysis, Academic Press, 1963, pages 559-563, it has been proposed to provide a rotatable shutter having a single slot-shaped aperture over a cuvette to control the incidence of light on an associated photomultiplier tube. This arrangement is applicable to bioluminescence and chemiluminescence applications only, since it does not provide for simultaneously controlling the light from the excitation lamp required for exciting the sample to fluorescence in fluorometric applications.
Accordingly, it is a general object of the present invention to provide a new and improved fluorometric analyzer wherein samples may be changed without exposing the light detector thereof to incident or reflected light.
It is a more specific object of the present invention to provide a new and improved head assembly for a fluorometric analyzer wherein a sample may be conveniently changed or adjusted without exposing the light detector of the analyzer to incident or reflected radiation.